Sample size calculations are a necessary part of research. The presentation will provide a tutorial on sample size calculations. In the first part of the talk I will review Type I and Type II error rates, power and sample size. Cautions for sample size calculations including effect size and pilot studies will be discussed. I will review some of the software programs available for sample size calculations. The types of studies discussed include cross sectional, longitudinal and cluster sampling. In the second part of the talk I will provide an example of a sample size calculation for a longitudinal study with attrition and cluster sampling.